Antipsychotics induce significant weight gain which increases the risk of chronic health problems such as diabetes, metabolic syndrome and cardiovascular disease. Antipsychotics-induced weight gain contributes to medication non-compliance which results in psychotic relapse. Additionally, the mortality risk of patients suffering from mental disorders is much higher than the general population and 60% of these deaths are due to the chronic health problems associated with obesity. Since obesity is a critical element in the progression towards the development of diabetes, metabolic syndrome and cardiovascular disease, it is important to determine the mechanisms by which antipsychotics induce weight gain. In this R36 project, I propose a novel hypothesis that antipsychotics induce weight gain by altering fructose absorption and metabolism in the intestine. The hypothesis is based on the following observations- (1) The target receptors for antipsychotics including dopamine, serotonin and histamine receptors are expressed in the intestine; (2) our preliminary result that chronic clozapine treatment increases intestinal fructose uptake in C57BL/6 wild type mice; (3) our preliminary result that wild type C57BL/6 mice show significant weight gain following chronic clozapine treatment; however, GLUT5 null mice of the same genetic background fail to show any clozapine-induced weight gain under the same experimental paradigm. Together our preliminary results strongly suggest that the intestinal GLUT5 fructose transporter is involved in clozapine-induced weight gain. In this project, I will determine the molecular mechanism by which, the atypical antipsychotic clozapine, induces weight gain. I will focus on the mechanisms by which enteric dopamine receptors regulate GLUT5 fructose transporter function and how clozapine modulates the expression of genes involved in the intestinal gluconeogenic and lipogenic pathways. All studies will be done using GLUT5 null mice and wild type littermates of the same genetic background. The results from this project will identify a novel role for antipsychotics in modulating intestinal fructose transport and metabolism. Identifying novel molecular mechanisms involved in the gut sensing of atypical antipsychotics may lead to break through therapies that will lead to improved antipsychotics. This will help improve the quality of life of those suffering from neuropsychiatric disorders and rely on these medications. This R36 dissertation proposal addresses an area of high priority for the Division of Adult Translational Research and Treatment Development at NIMH as it delineates the mechanisms through which specific psychotropic medications produce adverse metabolic and cardiovascular events.